This invention relates to electric controllers and more particularly to an electric controller for supplying power to, for example, electric brake systems to be used by a towed vehicle when being pulled by a towing vehicle.
Recreational and utility trailers adapted to be towed by automobiles and small trucks and many similar towed vehicles are commonly provided with electric brakes. The electric brakes generally comprise a pair of brake shoes which, when actuated, frictionally engage a brake drum. An electromagnet is mounted on an end of a lever which actuates the brake shoes. When an electric current is applied to the magnet, the magnet is drawn against the rotating brake drum which pivots the lever for actuating the brakes. The braking force is proportional to the electric current applied to the magnet. Controls for electrically operated brakes must be easily adjustable to accommodate different relative weights of the towed and towing vehicles. The controls further must be predictable to give the driver of the towing vehicle a feeling of smooth control and positive brake operation both upon applying the braking effort to the towing vehicle and also upon releasing the braking effort.
The braking system for the towed vehicle typically is actuated either in response to hydraulic pressure in the braking system of the towing vehicle or in response to the pressure applied by a driver's foot on a transducer mounted on the towing vehicle's brake pedal or in response to a manually operated control. In one type of electronic control for electrically operated brakes, a pulse modulator generates a pulsating voltage having a pulse width which is varied with the amount of braking effort desired for the towed vehicle. The electronic control is protected against short circuit conditions in the circuit for the brake actuating magnets. In the event of a sudden short circuit, the pulse output from the pulse modulator is disabled to protect the circuit. The pulse output may be disabled for several pulses and then reestablished to determine if the short circuit condition was momentary or if it still exists. Circuitry of this type for protecting against short circuits in the output of an electronic brake control works quite well for protecting the control in the event of sudden and complete short circuits. However the circuit is not designed to handle partial short circuits which act as a resistance and causes a higher than normal output current from the brake control which is below the level which causes an interruption in output from the control.